The present invention relates to an apparatus for determining the energy of charged particles, particularly of electrons separated from a sample by bombardment with ionizing radiation, the apparatus including an evergy analyzer as well as an electron-optical system disposed between the sample and the energy analyzer and containing a deceleration path for the charged particles to be analyzed.
In order to perform electron spectroscopy for chemical analysis (ESCA), it is common practice to bombard the sample to be tested with ionizing radiation. The energy of the electrons thus separated from the surface of the sample is then measured. The recorded energy spectrum of the electrons indicates the chemical composition of the surface of the sample. The energy of the electron leaving the sample can be measured between 2 and 1487 electron volts. When using the AL- Kd radiation for excitation. For other excitation-energys, the margin will have other limits.
German Offenlegungsschrift (Laid-Open Patent Application) No. 1,948,757 discloses a system for decelerating the electrons emanating from the sample directly in the vicinity of the sample and for guiding them through an annular gap to an energy analyzer. The deceleration effects an improvement in the properties, particularly the resolution, of the electronspectrometer disclosed in German Offenlegungsschrift (Laid-Open Patent Application) No. 1,948,757. However, this known electronspectrometer has the drawback that the immediate vicinity of the sample is not free of fields. Thus, it is impossible to perform other experiments simultaneously with the same sample or to perform successive analyses of the sample merely by switching instruments without modifying them.
Furthermore, the distance between the sample and the analyzer is very small. It is therefore difficult to define the aperture opening from outside the analyzer.
It is a further drawback that the particles, which may be electrons, photons, fast neutral particles, or sputter dirt, enter the analyzer with high energy and may there produce stray electrons which then contribute to an increased noise background in the energy spectrum.